1. Field of the Invention
This invention pertains generally to progressing cavity positive displacement pumps, and more particularly to drive arrangements for progressing cavity pumps which have internalized speed reducing means.
2. Description of the Background Art
Progressing cavity or helical pumps are used for positive displacement of fluids. These pumps are widely used in commercial and industrial settings, frequently for submersible pumping applications. Progressing cavity pumps typically involve a rotor of helical contour that rotates within a matching stator. The rotor generally has one or more helices or lobes, while the stator has matching helices, with the stator having one more helix than the rotor, so that the ratio of rotor helices to stator helices is n/n+1. Cross sectional profiles of the rotor and stator of progressing cavity pumps are typically hypocycloidal, although involute or other profiles are feasible.
In progressing cavity pumps, the pump rotor centerline is eccentrically disposed relative to the centerline of the stator, typically by one unit of eccentricity. In operation, the rotor is rotated by external actuating means about its own centerline within the stator. As the rotor rotates, it also orbits about the centerline of the stator. If rotor rotation is clockwise, then its orbital motion within the stator is in a counterclockwise direction, and vice versa. The ratio of orbital rotation to axial rotation depends on the number of helices in the rotor and stator. The helices of the rotor and stator are shaped so that pockets of fluid are formed within the pump. The fluid pockets are moved (positively displaced) as the rotor rotates and orbits within the stator.
Since the rotor centerline is eccentric relative to the stator centerline and the rotor undergoes axial and orbital rotation movement at the same time, the rotor ends describe a nutating motion relative to the stator and pump housing. Because of this nutating motion of the rotor ends, however, the rotor cannot be directly actuated by an external drive shaft. Therefore, various drive arrangements and methods for cavity pumps have been devised to accommodate the nutating motion of the rotor. One common drive arrangement used to overcome this difficulty employs universal joints to provide power to the rotor. Other approaches have involved use of connecting rods with either pin joints or gear joints to simulate universal joints. Another method is use of a splined eccentric shaft together with allowing the stator to rotate about its own axis. Yet another approach has been to employ a flexible shaft rather than attach the shaft to universal joints.
For example, U.S. Pat. No. 4,482,305 discloses an axial flow apparatus with rotating helical chamber and spindle members which use a gear arrangement. U.S. Pat. No. 4,273,521 discloses a drive arrangement wherein gears are used to avoid the need for a universal joint. U.S. Pat. No. 4,237,704 discloses an Oldham type coupling and pump embodying the same. U.S. Pat. No. 3,982,858 discloses a segmented stator for a progressive cavity transducer employing multiple segmented stator elements connected in series, together with a universal joint. U.S. Pat. No. 3,938,915 discloses a screw rotor machine with a hollow thread rotor enclosing a screw cam rotor in which a pump has a shaft which is eccentric relative to the centerline of the rotor. U.S. Pat. No. 3,307,486 discloses a universal joint and sealing means for screw pumps, employing a universal joint. U.S. Pat. No. 2,545,604 discloses a pump using a floating drive link. Australian Patent No. 2,545,604 discloses a rotor having eccentrically placed journals on each end of the stator member. German Patent No. 2,645,933 discloses an eccentric helical rotor type positive displacement pump employing universal linkings.
As can be seen therefore, a variety of drive arrangements have been devised for use with progressing cavity or helical pumps. However, several deficiencies have become apparent in the currently known drive arrangements. Since a large number of moving parts are required for these drive arrangements, substantial space, typically in the form of an external gearbox, must be committed to the drive arrangement, thus increasing the overall size of the pump systems. Particularly, the connecting rods associated with universal joints can substantially increase the overall length of the pump. Additionally, the large number of moving parts experience wear and eventually fail, resulting in mechanical problems which increase with the complexity and number of parts in the drive arrangement. Contaminants present in the fluids transported by progressing cavity pumps tend to work into the gears and joints of the pump drive systems, further accelerating wear and failure of parts.
Yet another drawback in the background art involves electric motors used to drive submersible progressive cavity pumps. These electric motors commonly deliver high rotation speeds, generally around 3600 RPM for small electric motors. Since submersible progressive cavity pumps generally operate at substantially lower rates of rotation, external means for rotational speed reduction must be included with the pumps, generally in the form of an external gearbox.
Therefore, there is a need for a drive arrangement for progressive cavity pumps which is simple and compact, experiences reduced wear and failure, and which does not require an external gearbox to reduce the rotational speed delivered to the pump. The present invention satisfies these needs, as well as others, and overcomes the deficiencies found in prior drive arrangements.
The foregoing patents reflect the state of the art of which the applicant is aware and are tendered with the view toward discharging applicant's acknowledged duty of candor in disclosing information which may be pertinent in the examination of this application. It is respectfully stipulated, however, that none of these patent teach or render obvious, singly or when considered in combination, applicant's claimed invention.